Data centers often contain a vast number of computers (i.e., servers). Many of these servers are temporarily underutilized or even unused, but are maintained to handle surges in requests arriving at the data center. For example, consider the Christmas rush at online shopping sites or the late afternoon congestion at a commuter traffic information site. The servers currently used in data centers consume a large amount of energy even when they are idle (for some servers, idle is 70% of full energy usage). Turning these servers off could save energy, but it also could adversely affect the response time of a web service if a surge of customers arrive and not enough servers are powered on. The present concepts can manage data centers in a manner that satisfies request service response times while considering energy usage of the data center.